HPHT Synthesis And Performance Of Fe,Ni Doped CoSb₃ Thermoelectric Materials

Thermoelectric materials are energy materials that realize thermal-to-electrical direct conversion using the Seebeck effect and Peltier effect.It is an important application in industrial waste heat generation,small temperature difference generation,space special power supply,rapid cooling and temperature control.The performance of the thermoelectric material is characterized by the dimensionless ZT = T?S2 / ?,where S is the Seebeck coefficient,? is the electrical conductivity,? is the thermal conductivity,and T is the absolute temperature.The Seebeck coefficient and conductivity are determined by the electronic structure of the material and the carrier transport properties,with intrinsic correlation.The thermal conductivity is closely related to the thermal conductivity?electron thermal conductivity?,and also depends on the phonon transport properties?lattice thermal conductivity?determined by the chemical composition and microstructure of the material.Normally,the lattice thermal conductivity is a main factor.Optimizing the performance of thermoelectric materials is mainly the synergistic regulation of these interrelated physical properties.Although the low conversion efficiency and high cost of existing thermoelectric materials have limited its wide range of applications,with the upsurge of thermoelectric research in the world,the research on thermoelectric theory has been deepening and benefiting from the development of material preparation,The performance of thermoelectric materials has been greatly improved.The ideal thermoelectric material may have the properties of the "phonon glasselectron crystal" proposed by Slack,namely,crystal-like electron transport properties,and glass-like phonon transport properties.Skutterudite material not only has such a nature,play an independent regulation of electron transport and phonon degree of freedom of the role;and it contains the intrinsic lattice,impurity atomic filling,can not affect the electrical performance at the same time,Promoting phonon scattering,reduce the material lattice thermal conductivity,and ultimately optimize the thermoelectric properties.Its considerable thermoelectric properties is now generally considered to be the most promising thermoelectric materials.High temperature and high pressure synthesis method has the following advantages: 1.High pressure can improve the reaction rate and product conversion rate,reduce the synthesis temperature at the same time,can significantly reduce the synthesis time;2.The existence of high pressure phase in the atmospheric pressure method is difficult to prepare of the material can be successfully synthesized;3.High pressure can increase the density of materials,symmetry,coordination number,shorten the role of key length;4.High pressure can be easily obtained pure phase material,to improve the crystallinity problem;5.The high pressure phase can also promote the decomposition of the compound and the reaction of the compound;6.Under high pressure,it can not only inhibit the reaction of the compound,but also can promote the oxidation reaction,so as to obtain the compound with high oxidation state.Amorphous conversion process,and can promote the process of amorphous conversion and so many advantages,so high temperature and high pressure equipment is more expensive,but the optimization,improve the material has unparalleled advantages,as well as the synthesis process of many degeneration,resulting in high temperature and high pressure method exploring the application value of thermoelectric materials.In this work,the use of high temperature and high pressure method of the other cobalt-based thermoelectric materials were Co site replacement,replacement elements are: Ni,Fe element.In a series of experiments in which the single element Ni was replaced with Co,the optimum synthesis time was 20-30 min and the detailed analysis was performed.The results of XRD showed that Nix Co4-x Sb₁₂?x = 0.025,0.05,0.1,0.15,0.25?was good at the synthesis pressure of 1GPa.The grain of the samples were observed well under the scanning electron microscope.In high-resolution transmission electron microscopy can be found in the sample there are a lot of micro-defects.The results of thermoelectric test show that the absolute value and resistivity of Seebeck coefficient decrease with the increase of Ni concentration at room temperature.Within the pressure range of the study,the absolute value and resistivity of the Seebeck coefficient of the sample increase as the synthesis pressure increases.When the synthesis pressure is 1GPa,the maximum power factor can reach 9 × 10-4m-1K-2.For the best temperature performance at room temperature,compared with the pure temperature of Co Sb₃,it can be found that: When the pressure is 1GPa,Ni_0.15Co_3.85Sb₁₂ is N-type semiconductor.2.Electron transport performance and thermal transport performance were optimized by Ni element replacement to Cobalt pyroelectric materials.At a temperature of 600 K,the maximum ZT value was 0.52.Fe_yNi_0.15Co_3.85-y Sb₁₂?y = 0.2,0.25,0.3?was prepared by the method of substituting the double element Fe and Ni into the Co site of the dopant.At room temperature sample Fe_y Ni_0.15Co_3.85-y Sb₁₂,different displacement of Fe elements into the cobaltbased thermoelectric materials and different synthetic pressure of the electrical transport performance.After the sample was selected,the sample Fe_0.2Ni_0.15Co_3.65Sb₁₂ was subjected to the thermoelectric transport performance test with the pressure of 1GPa.The electrical transport of the sample Fe_0.2Ni_0.15Co_3.65Sb₁₂ was carried out in the temperature range.The performance of the sample is lower than that of the Ni_0.15Co_3.85Sb₁₂,and the highest power factor is 14.76?10-4Wm-1K-2.The thermal transport properties of the sample Fe_0.2Ni_0.15Co_3.65Sb₁₂ are slightly lower than that of the sample Ni_0.15Co_3.85Sb₁₂.The dimensionless dimension factor ZT of the sample Fe_0.2Ni_0.15Co_3.65Sb₁₂ at the temperature of 700 K is calculated as 0.35.The experimental results show that the high temperature and high pressure method can be used to improve the electrical properties of the material,and the thermal conductivity of the material can be reduced obviously.Finally,the cobalt thermoelectric properties.